1. Field of the Invention
The invention relates to a needle receiving hole member guide mechanism for a zigzag sewing machine and more particularly relates to a mechanism for guiding a needle hole member along a laterally elongated hole of a predetermined range formed in a needle plate, in which a vertically reciprocating needle is laterally swung so that zigzag stitches of variable amplitudes may be formed. The mechanism is so structured and operated in synchronism with an upper thread carrying needle to draw out a desired amount of a lower thread required for formation of various types of stitches.
2. Prior Art
As well known in the industrial field, the conventional zigzag sewing machine has a laterally elongated needle hole formed in the needle plate thereof so that a vertically reciprocating and laterally swingable needle may constantly drop one point to form straight stitches and also may be laterally swingable from minimum to maximum to from zigzag stitches of variable amplitudes. However as shown in FIG. 11 depicting the positional relationship between the needle and a fabric or cloth in a conventional zigzag sewing machine, when a needle 17 pierces through the fabric 6 placed on a laterally elongated needle hole 18a, the fabric 6 is pushed into the needle hole by the needle 17 and the fabric is slacked down within the needle hole. On the contrary, as shown in FIG. 12, the fabric will be lifted up above the needle plate 18 as needle goes up. Such flapping phenomena of the fabric will fail to make a desired thread loop as the needle goes up as shown in FIG. 14 because there is no sufficient friction between the fabric and the needle. It is apparent that loop taker 28 often fails to catch the thread loop, resulting in skipped stitches.
Consequently, it is therefore desirable to provide a round needle hole of a diameter which is just slightly larger than that of a diameter of the needle 17 as generally known in a straight stitch sewing machine and shown in FIG. 13 and FIG. 14, so as to eliminate the above mentioned defects and disadvantages.
In this respect, published Japanese utility model 56(1981)-43271 discloses a laterally elongated hole 18a formed in a needle plate 18 and a member having a round needle hole is in engagement with the hole 18a and is reciprocated therein in synchronism with the swinging movement of the needle 17 as shown in FIG. 15.
The present invention has been provided to solve shortcomings of the prior art and to further improve the mechanism of the published Japan Utility Model 56(1981)-43271. In the zigzag sewing machine according to the present invention, the mechanism of the mentioned published Utility Model application has been appropriately modified to draw out a lower thread of an amount required for each of various stitches to be formed.
Originally, a draw-out amount of the lower thread must be suitably changed in consideration of given conditions, such as a thickness of fabric to be sewn, a type of thread to be used, and types of patterns to be stitched by a zigzag sewing machine. In the conventional sewing machine, however, the lower thread is drawn out with a constant amount by a up-and-down movement of a drawing member operated in association with a feed dog which may be adjusted to change the feeding amount of the fabric, that is to change the stitch length.